Explosive composition



United Sates atent 3,093,521 EXPLGSIVE (IQMPUSETIQN Cyril .l. Breza, Thorofare, NJ, assignor to E. I. du Pont de Nemours and Company, Wilmington, Del, 2 corporation of Delaware No Drawing. Filed Get. 26, 1960, Ser. No. 65,012 3 Claims. (til. 149-19) The present invention relates to a novel deformable, self-supporting explosive composition. More particularly, this invention relates to a deformable, self-supporting explosive composition having a high density, and an adequate detonation sensitivity when unconfined and in thin layers and characterized especially by a relatively low velocity of detonation.

Recent advances in the art of harnessing explosivelygenerated pressures for constructive rather than destructive purposes have been largely in the field of metal treating and working. U.S. Patent 2,703,297, issued March 1, 1955, to N. A. MacLeod, for example, describes a process for .the hardening of austenitic manganese steels with the shock wave which results from detonation of a thin layer of explosive placed against the surface of the steel article. Such developments as this have created a real need for readily deformable, self-supporting explosive compositions which can be easily formed into basic shapes, such as sheets and tubes, that are uniform in cross-section and will not fail to shoot when unconfined even in thin sections.

Substantial progress in fulfilling this need has been made by workers in the art. For instance, there is described in U.S. patent application Serial No. 46,044, filed August 17, 1960, in the names of C. J. Breza and C. 0. Davis now US. Patent No. 2,999,743 (having a common assignee with the present application), a flexible, self-supporting sheet explosive composition which is well suited for use in the performance of various explosive metal treating processes, such as the aforesaid steel hardening process of MacLeod. The Breza and Davis sheet explosive consists of 7092.5'% of :a high explosive compound, which may be either PETN or RDX, in admixture with a binding agent formed of an organic rubber and a thermoplastic terpene hydrocarbon resin. This sheet explosive has a detonation velocity of about 7000 meters/ second. While such a composition may be fine for the explosive austenitic steel hardening process of MacLeod, some of the more recent developments in the explosive metal treating field require a much slower explosive, i.e., a deformable, self-supporting high exp-losive in sheet form or the like with a much lower detonation velocity.

For example, US. patent application Serial No. 65,194, filed October 26, 1960, in the names of G. R. Cowan, I. I. Douglass, and A. H. Holtzman (having a common assignee with the present application), describes an explosive metal cladding process which requires a high explosive sheet that detonates at a velocity not greater than 120% of the sonic velocity of any of the metals in the system. This corresponds in most cases to a high explosive sheet composition having a detonation velocity of 6000 meters/sec. or less. In some cases (depending upon the metals involved), this explosive metal cladding technique requires a sheet explosive composition with a detonation velocity as low as 3000 meters/ second or lower which represents less than half the detonation velocity of the sheet explosive described in the aforementioned Breza and Davis application. And notwithstanding this relatively low velocity of detonation for a high explosive detonating composition, the composition must be capable of sustaining the detonation without confinement even in relatively thin cross-sections (one-half inch, or less).

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A sheet explosive composition having the foregoing properties and characteristics is not taught by the prior art. The provision of such a composition is accordingly the principal objective of the present invention.

In attaining this objective, I have sought to prepare a readily deformable, self-supporting sheet explosive composition having all the physical and functional advantages of the Breza and Davis product referred to above along with the substantially lower detonation velocity. In this sense, the novel explosive composition of the present invention may be considered an improvement or a refinement of the Breza and Davis composition especially intended for those end-uses requiring a slow explosive.

My novel explosive contains 15-45% by weight of the high explosive (erg. PETN or RDX), 1020% by weight of the rubber/terpene resin binder, and a substantial proportion (30-75%) by weight of red lead, i.e. lead tet-roxide.

The essence of my invention is the discovery that red lead has the unique and unpredictable property as a diluent in compositions of this type of substantially reducing the detonation velocity of the material without adversely affecting its sensitivity, its ability to propagate a detonation, and/ or its advantageous physical properties. Since the unmodified composition, i.e. the composition disclosed by Breza and Davis requires at least about 70% by weight of the explosive to insure satisfactory explosive properties, it is very surprising that compositions of this type doped up with large amounts of red lead will continue to perform satisfactorily with as little as only 15% of the explosive. In this environment, red lead exhibits a peculiar and remarkable ability to greatly extend the sensitivity and propagate-ability properties of the explosive while at the same time vastly depressing the rate at which the explosive will propagate a detonation.

The following examples serve to illustrate specific embodiments of the explosive composition of the present invention. The parts given in the examples are parts by weight unless otherwise specified. The thermoplastic terpene hydrocarbon resin used in all the examples was Piccolyte, a commercially available material composed of polymers of ,G-pinene.

Example 1 In a sigma-blade mixer heated with water at F. 20 parts (dry basis) of water-wet PETN of particle size within the range of 0.1 to 10 microns and with an average maximum particle dimension of 0.1 to 2.0 microns was mixed with 22.2 parts of a hexane solution containing 10 parts of a 50/50 mixture of the terpene resin (Piccolyte S-l0 and 8-70 grades) and butyl rubber. After complete blending of the mixture was obtained, the water present on the surface of the mass was decanted. Red lead (pigment grade) in the amount of 70 parts was then added to the mass, and mixing was continued until all the hexane and water had been evaporated from the mass. The solvent-free mass was removed from the mixer, pressed into l inch pads, and the pads were rolled between aluminum rollers into sheets.

The sheets had a density of 3.22 grams per cc. and had an impact sensitiveness, as determined by the standard drop test (S-kg. weight), of 17 inches (50% detonation point). The sheet was readily initiated by a standard No. 6 blasting cap, and the velocity of detonation was 4100 meters per second. The detonation propagated reliably in all sheets of 0.1 inch thickness and greater. The sheets were strong and flexible and when bent or otherwise shaped, they retained their shape.

Example 2 A series of mixes was prepared in accordance with 3 the method described in Example 1, with the exception that the relative proportions of PETN, binder, and red lead were varied. The properties of sheets prepared from these mixes were summarized in the following table.

All of the sheets were strong, flexible, self-supporting and could be initiated by No. 6 caps.

Example 3 Sheets Were prepared from a mix prepared as described in Example 1 except that a butadiene-styrene copolymer (commercially available as Pliofiex 106) was substituted for the butyl rubber. These sheets displayed properties virtually equivalent to those of Example 1.

Example 4 The procedure of Example 1 is repeated except that 10 parts of a 50/50 mixture of the terpene resin and natural rubber is substituted for the terpene resin/butyl rubber binder. The resultant explosive sheets obtained possess physical and explosive properties comparable to the product of Example 1 Example 5 The procedure of Example 1 is repeated except that parts of a 50/50 mixture of the ter-pene resin and neoprene is substituted for the terpene resin/butyl rubber binder. The resultant explosive sheets obtained possess physical and explosive properties comparable to the product of Example 1.

As is apparent from the foregoing examples, the novel compositions of the present invention may be conveniently prepared by admixing the high explosive component with an organic solvent solution of the rubber/terpene resin binder followed by addition of the red lead and evaporation of the solvent. The resultant dry, solvent-free composition is tough, cohesive, workable, and of slight resilience. It is easily formed by pressing, extruding, molding, and rolling, etc. into useful shapes such as sheets, cords, tubes and the like, and supports itself in any shape or configuration into which it is formed. The method of manufacture of the composition and/or the manner in which it is fabricated into useful shapes form no part of the present invention; any suitable techniques being satisfactory.

Thermoplastic terpene resins are readily available in either solid form or in solution. These resins are prepared in a well-known manner by the polymerization of ,B-pinene containing minor amounts of a-pinene and dipentene in the presence of a Friedel-Crafts catalyst, such as anhydrous aluminum chloride, according to the techniques described in detail by Kirk-Othmer, Encyclopedia of Chemical Technology, Interscience Publishers, Inc. (1954), vol. 13, pages 7023. The resins have the empirical formula (C H wherein n represents the degree of polymerization. The latter may be varied over a Wide range to yield polymers of low or of relatively high average molecular Weights. Resins having average molecular weights as high as 1200 to 1250 are known; such resins having a softening point in the range of 125 135 C. The softening point is, of course, a function of average molecular weight and thus characterizes a particular resin in this regard. The various grades of the well-kown Piccolyte resins are designated in this manner and the softening points of Piccolyte S -10 and Piccolyte" S-70 thus are 10 C. and 70 C., respectively. These particular Piccolyte resins are very convenient to work with and yield an explosive composition of the type described having excellent workability and other physical properties in line with the objectives of the invention. The use of these particular resins is by no means critical to the invention, however, and the novel compositions of the present invention may be prepared with any grade of Piccolyte or other hydrocarbon terpene resin.

The red lead constitutes 30 to of the explosive composition. The use of greater amounts of this component in my compositions may adversely affect sensi tivity whereas the use of lesser amounts may result in elevation of the velocity of detonation to an undesirably high figure. Obviously, it is essential that the red lead be distributed evenly throughout the composition. Because of its availability, relatively uniform particle size, and convenient handling properties, that form of red lead known as pigment grade is preferred.

While the use of PETN as the cap-sensitive crystalline high explosive has been demonstrated in the examples, the use of other cap-sensitive crystalline explosives is equally feasible. For example, other organic nitrates, such as nitromannite, nitramines, such as RDX, HMX, and ethylene dinitramine, and *azides, such as lead azide, as Well as mixtures of two or more explosive compounds also can be used.

The foregoing examples illustrate preparation of the explosive products of the present invention with a variety of different organic rubbers. The precise chemical nature of the latter is of no significance whatever insofar as the present invention is concerned. The rubber is used solely because of its physical, i.e. rubbery properties, and thus any organic rubber composition may be used in preparing the novel explosive products of the present invention. Suitable materials include both natural rubber and synthetic rubbers, such as GRS rubber or polyisobutylene, neoprene, polysulfide rubber (commercially available as Thiokol), Buna N, butyl rubber, polyisoprene, nitrile rubber, polyurethanes, chlorosulfon'ated polyethylene (commercially available as Hypalon S-2), etc.

Having fully described the invention, I intend to be limited only by the following claims.

I claim:

1. A deformable self-supporting, low-velocity explosive composition consisting essentially of by weight 15 to 45% of a finely-divided cap-sensitive crystalline high explosive compound, selected from the group consisting of organic nitrates, organic nitramines and azides, 30 to 75% of red lead, and 10 to 25% of a binder consisting of 25 to 75 of an organic rubber material selected from the group consisting of natural and synthetic rubber, and 75 to 25% of a thermoplastic terpene hydrocarbon resin.

2. A tough, thin, flexible, self-supporting high explosive sheet consisting essentially of a thin layer of the explosive composition of claim 1.

3. A deformable self-supporting, low-velocity explosive composition consisting essentially of by Weight 15 to 45% of finely-divided pentaerythritol tetranitrate, 30 to 75 of red lead and 10 to 25 of a binder consisting of 25 to 75% of butyl rubber and 75 to 25 of a thermoplastic terpene hydrocarbon resin having a softening point of about from 10 to 70 C.

References Cited in the file of this patent UNITED STATES PATENTS 2,839,374 Taylor et a1 June 17, 1958 FOREIGN PATENTS 584,547 Great Britain Jan. 17, 1947 OTHER REFERENCES Dempster: Discussions of the Faraday Society, No. 22, Cook, 1956, pp. 196-211. 

1. A DEFORMABLE SELF-SUPPORTING, LOW-VELOCITY EXPLOSIVE COMPOSITION CONSISTING ESSENTIALLY OF BY WEIGHT 15 TO 45% OF A FINELY-DIVIDED CAP-SENSITIVE CRYSTALLINE HIGH EXPLOSIVE COMPOUND, SELECTED FROM THE GROUP CONSISTING OF ORGANIC NITRATES, ORGANIC NITRAMINES AND AZIDES, 30 TO 75% OF RED LED, AND 10 TO 25% OF A VINDER CONSISTING OF 25 TO 75% OF AN ORGANIC RUBBER MATERIAL SELECTED FROM THE GROUP CONSISTING OF NATURAL AND SYNTHETIC RUBBER, AND 75 TO 25% OF A THERMOPLASTIC TERPENE HYDROCARBON RESIN. 